Present invention relates to a printhead, a printing apparatus and a printing method using the printhead, more particularly to an ink-jet printhead used in a copying machine, a facsimile machine and a word processor, a printer used as an output terminal of a host computer, or a video printer, a printing apparatus and a printing method using the printhead.
FIGS. 11 and 12 respectively show the construction of a printhead of a conventional ink-jet printing apparatus, where electrothermal transducers and their driving circuits are formed on one circuit board, as disclosed in Japanese Patent Application No. 3-194118.
In FIGS. 11 and 12, reference numeral 101 denotes electrothermal transducers (heaters) for generating thermal energy; 102, power transistors for supplying an electric current of a predetermined voltage to the electrothermal transducers 101; 103, a time-divisional logical circuit for time-divisionally controlling power-supply to the power transistors 102 so as to time-divisionally heat the electrothermal transducers 101; 104, latches for holding serially-inputted print information for the electrothermal transducers; 105, a shift register for storing serially inputted data which indicates whether or not supply electric current to the respective electrothermal transducers 101 for discharging ink; 106, a power line for applying a predetermined voltage to the electrothermal transducers 101; and 107, a switch for supplying the print information latched at the latches 104 to the power transistors 102.
Note that the number of data bits as print information stored in the shift register 105 is the same as the number of the electrothermal transducers 101 and that of the power transistors 102. Further, the electrothermal transducers 101 are logically divided into a plurality of groups for the printing operation.
Also in FIGS. 11 and 12, as input terminals of various control signals to be supplied to the printhead, numeral 201 denotes a data input terminal for inputting print information (DATA); 202, a transfer-clock input terminal for inputting a transfer clock (CLK) for the shift register 105; 203, a latch-signal input terminal for supplying a latch timing signal (LATCH) to the latches 104; 204, a heater-enable signal input terminal for inputting a heater-enable signal (H.ENB) to determine timing for supplying the electric current to the respective electrothermal transducers 101; and 205, a selection-signal input terminal for inputting a selection signal (SEL) to select one of the groups of the electrothermal transducers 101.
FIGS. 13A-13C comprise a timing chart showing the various control signals for driving the circuits of the printhead as shown in FIGS. 11 and 12. The operation of the circuits in FIGS. 11 and 12 will be described with reference to FIGS. 13A-13C.
First, the transfer-clock input terminal 202 inputs a transfer clock (CLK). The shift register 105 performs data transfer in synchronization with the rising edge of the transfer clock (CLK). Print information (DATA) to turn on/off the respective electrothermal transducers 101 is supplied from the data input terminal 201. As the number of data bits storable in the shift register 105 is the same as the number of the electrothermal transducers 101 and that of the power transistors 102, the transfer-clock input terminal 202 inputs the transfer clocks (CLK's) of the number of the electrothermal transducers 101, to transfer the print information (DATA) to the shift register 105. Then, the latch-signal input terminal 203 inputs a latch signal (LATCH) to hold the print information corresponding to the respective electrothermal transducers 101 in the latches 104.
Thereafter, in the printhead having the construction as shown in FIG. 11, when the heater-enable signal input terminal 204 of the time-divisional logical circuit 103 receives a heater-enable signal (H.ENB) and the selection-signal input terminal 205 of the time-divisional logical circuit 103 receives a selection signal (SEL) at appropriate timings, the electric current is supplied to the power transistors 102 and then the electrothermal transducers 101 while the signals H.ENB and the SEL are turned on, thus ink droplets are discharged in accordance with the print information.
In the printhead having the construction as shown in FIG. 12, when the switch 107 is closed at appropriate timing, the electric current is supplied to the power transistors 102 and the electrothermal transducers 101 in correspondence with the time where the switch 107 is closed, thus ink droplets are discharged in accordance with the print information.
However, the above conventional constructions have the following problems:
(1) As the number of data bits storable in the shift register and the number of the latches are the same, the shift register and the latches occupy large space on the circuit board, thus preventing downsizing of the circuit board and reduction of production costs. PA1 (2) As a printhead must always be capable of printing at a high-printing density, it is necessary, on the limited space on the circuit board of the printhead, to reduce the number of electric devices per pixel (bit) printing. To meet this requirement, the respective circuits as the-parts of the printhead must be further miniaturized. The electrothermal transducers, the power transistors and the switches are single-tip devices and therefore suitable for microminiaturization. The latches can also be easily miniaturized since these circuits comprise a relatively small number of constituent devices. However, in the shift register for storing information of a predetermined number of data bits, corresponding to the number of the electrothermal transducers, the power transistors, the switches and the latches, a large number of constituent devices per pixel printing are required. Since the number of devices must correspond to the number of electrothermal transducers, downsizing of the shift register is difficult.
To solve this problem, the relation between the number of data bits (A) and the number of latches (B) may be A:B=1:n, and the shift register may be operated n times. Then, the space occupied with the devices necessary for the shift register can be reduced. However, this requires n latch-clock input terminals for operating the latches, and increases the number of wires for electrically connecting the lead frame with external devices. Finally, this increases the number of assembling steps of the printhead, and thus increases the production costs.
Upon realizing a multifunctional printhead in consideration of future technological improvement, a complicated combination of a lot of logical circuits is required for inputting variety of data, and for the data input, the logical circuits must have external input terminals. That is, the multifunctional printhead needs a lot of input terminals, which increases the number of assembling steps and production costs. Accordingly, it is preferable to reduce the number of input terminals to a minimum.